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DNS

As of Kuma version 1.2.0, DNS on the data plane proxy is enabled by default on Kubernetes. You can also continue to deploy with DNS on the control plane.

Data plane proxy DNS

In this mode, all name lookups are handled locally by the data plane proxy. This approach allows for more robust handling of name resolution.

On Kubernetes, this is the default. You must enable it manually on universal deployments.

Universal

In Universal mode, the kumactl install transparent-proxy and kuma-dp processes enable DNS resolution to .mesh addresses.

Prerequisites:

  • kuma-dp, envoy, and coredns must run on the worker node – that is, the node that runs your service mesh workload.
  • core-dns must be in the PATH so that kuma-dp can access it.
    • You can also set the location with the --dns-coredns-path flag.
  • User created to run the kuma-dp process. You must run the kuma-dp process with a different user than the user you test with. Otherwise, name resolution might not work.
    • On Ubuntu, for example, you can run: useradd -U kuma-dp.

  1. Specify the flags --skip-resolv-conf and --redirect-dns in the transparent proxy iptables rules:

    kumactl install transparent-proxy \
          --kuma-dp-user kuma-dp \
          --kuma-cp-ip <kuma-cp IP> \
          --skip-resolv-conf \
          --redirect-dns

  2. Start the kuma-dp

    kuma-dp run \
  --cp-address=https://127.0.0.1:5678 \
  --dataplane-file=dp.yaml \
  --dataplane-token-file=/tmp/kuma-dp-redis-1-token

    The kuma-dp process also starts CoreDNS and allows resolution of .mesh addresses.

Special considerations

This mode implements advanced networking techniques, so take special care for the following cases:

How it works

The data plane proxy DNS consists of:

  • an Envoy DNS filter provides responses from the mesh for DNS records
  • a CoreDNS instance launched by kuma-cp that sends requests between the envoy filter and the host DNS
  • iptable rules that will redirect the original DNS traffic to the local CoreDNS instance

As the DNS requests are sent to the Envoy DNS filter first, any DNS name that exists inside the mesh will always resolve to the mesh address. This in practice means that DNS name present in the mesh will “shadow” equivalent names that exist outside the mesh.

Overriding the coreDNS configuration

In some cases it might be useful for you to configure the default coreDNS. To do so you can use --dns-coredns-config-template-path as an argument to kuma-dp. This file is a coreDNS configuration that is processed as a go-template. If you edit this configuration you should base yourself on the default existing configuration.

Control Plane DNS

The Kuma control plane deploys its DNS resolver on UDP port 5653. It allows decoupling the service name resolution from the underlying infrastructure and thus makes Kuma more flexible. When Kuma is deployed as a distributed control plane, Kuma DNS enables cross-cluster service discovery.

Kubernetes

When you install the control plane, set the following environment variable to disable the data plane proxy DNS:

KUMA_RUNTIME_KUBERNETES_INJECTOR_BUILTIN_DNS_ENABLED=false

Pass the environment variable to the --env-var argument when you install:

kumactl install control-plane \
  --env-var KUMA_RUNTIME_KUBERNETES_INJECTOR_BUILTIN_DNS_ENABLED=false

Universal

  1. Configure the transparent proxy iptables rules:

    kumactl install transparent-proxy \
          --kuma-dp-user kuma-dp \
          --kuma-cp-ip <KUMA_CP_IP_ADDRESS>

  2. Start the kuma-dp with flag --dns-enabled set to false:

    kuma-dp run \
  --cp-address=https://127.0.0.1:5678 \
  --dataplane-file=dp.yaml \
  --dataplane-token-file=/tmp/<KUMA_DP_REDIS_1_TOKEN> \
  --dns-enabled=false

Configuration

You can configure Kuma DNS with the config file, or with environment variables:

# DNS Server configuration
dnsServer:
  # The domain that the server will resolve the services for
  domain: "mesh" # ENV: KUMA_DNS_SERVER_DOMAIN
  # Port on which the server is exposed
  port: 5653 # ENV: KUMA_DNS_SERVER_PORT
  # The CIDR range used to allocate
  CIDR: "240.0.0.0/4" # ENV: KUMA_DNS_SERVER_CIDR

The domain field specifies the default .mesh DNS zone that Kuma DNS provides resolution for. If you change this value, make sure to change the zone value for kumactl install dns to match. These values must be the same for kube-dns or CoreDNS server to redirect relevant DNS requests.

The port field specifies the port where Kuma DNS accepts requests. Make sure this value matches the port setting for the kuma-control-plane service.

The CIDR field sets the IP range of virtual IPs. The default 240.0.0.0/4 is reserved for future IPv4 use IPv4 and is guaranteed to be non-routable. We strongly recommend to not change this value unless you have a specific need for a different IP range.

How Kuma DNS works

Kuma DNS includes these components:

  • The DNS server
  • The VIPs allocator
  • Cross-replica persistence

The DNS server listens on port 5653, responds to type A and AAAA DNS requests, and answers with A or AAAA records, for example <service>.mesh. 60 IN A 240.0.0.100 or <service>.mesh. 60 IN AAAA fd00:fd00::100. The default TTL is 60 seconds, to ensure the client synchronizes with Kuma DNS and to account for any intervening changes.

The virtual IPs are allocated from the configured CIDR, by constantly scanning the services available in all Kuma meshes. When a service is removed, its VIP is also freed, and Kuma DNS does not respond for it with A DNS record.

Kuma DNS is not a service discovery mechanism. Instead, it returns a single VIP that is assigned to the relevant service in the mesh. This makes for a unified view of all services within a single zone or across multiple zones.

Usage

Consuming a service handled by Kuma DNS from inside a Kubernetes container is based on the automatically generated kuma.io/service tag. The resulting domain name has the format {service tag}.mesh. For example:

<kuma-enabled-pod>curl http://echo-server_echo-example_svc_1010.mesh:80
<kuma-enabled-pod>curl http://echo-server_echo-example_svc_1010.mesh

A DNS standards compliant name is also available, where the underscores in the service name are replaced with dots. For example:

<kuma-enabled-pod>curl http://echo-server.echo-example.svc.1010.mesh:80
<kuma-enabled-pod>curl http://echo-server.echo-example.svc.1010.mesh

The default listeners created on the VIP default to port 80, so the port can be omitted with a standard HTTP client.

Kuma DNS allocates a VIP for every service within a mesh. Then, it creates an outbound virtual listener for every VIP. If you inspect the result of curl localhost:9901/config_dump, you can see something similar to:

    {
     "name": "outbound:240.0.0.1:80",
     "active_state": {
      "version_info": "51adf4e6-287e-491a-9ae2-e6eeaec4e982",
      "listener": {
       "@type": "type.googleapis.com/envoy.api.v2.Listener",
       "name": "outbound:240.0.0.1:80",
       "address": {
        "socket_address": {
         "address": "240.0.0.1",
         "port_value": 80
        }
       },
       "filter_chains": [
        {
         "filters": [
          {
           "name": "envoy.filters.network.tcp_proxy",
           "typed_config": {
            "@type": "type.googleapis.com/envoy.config.filter.network.tcp_proxy.v2.TcpProxy",
            "stat_prefix": "echo-server_kuma-test_svc_80",
            "cluster": "echo-server_kuma-test_svc_80"
           }
          }
         ]
        }
       ],
       "deprecated_v1": {
        "bind_to_port": false
       },
       "traffic_direction": "OUTBOUND"
      },
      "last_updated": "2020-07-06T14:32:59.732Z"
     }
    },

To define dynamic hostnames using specific tags or expose on a different port you should use virtual-outbounds.

Last Updated: 11/7/2024, 12:55:21 PM

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